Commit message: Unsquashfs: additional write outside destination directory exploit fix

An issue on github (https://github.com/plougher/squashfs-tools/issues/72)
showed how some specially crafted Squashfs filesystems containing
invalid file names (with '/' and '..') can cause Unsquashfs to write
files outside of the destination directory.

Since then it has been shown that specially crafted Squashfs filesystems
that contain a symbolic link pointing outside of the destination directory,
coupled with an identically named file within the same directory, can
cause Unsquashfs to write files outside of the destination directory.

Specifically the symbolic link produces a pathname pointing outside
of the destination directory, which is then followed when writing the
duplicate identically named file within the directory.

This commit fixes this exploit by explictly checking for duplicate
filenames within a directory.  As directories in v2.1, v3.x, and v4.0
filesystems are sorted, this is achieved by checking for consecutively
identical filenames.  Additionally directories are checked to
ensure they are sorted, to avoid attempts to evade the duplicate
check.

Version 1.x and 2.0 filesystems (where the directories were unsorted)
are sorted and then the above duplicate filename check is applied.

Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk>
CVE: CVE-2021-41072
CWE: CWE-200
Vulnerability description: squashfs_opendir in unsquash-2.c in Squashfs-Tools 4.5 allows Directory Traversal, a different vulnerability than CVE-2021-40153. A squashfs filesystem that has been crafted to include a symbolic link and then contents under the same filename in a filesystem can cause unsquashfs to first create the symbolic link pointing outside the expected directory, and then the subsequent write operation will cause the unsquashfs process to write through the symbolic link elsewhere in the filesystem.

Project: squashfs-tools

static struct dir *squashfs_opendir(unsigned int block_start, unsigned int offset,
	struct inode **i)
{
	squashfs_dir_header_2 dirh;
	char buffer[sizeof(squashfs_dir_entry_2) + SQUASHFS_NAME_LEN + 1]
		__attribute__((aligned));
	squashfs_dir_entry_2 *dire = (squashfs_dir_entry_2 *) buffer;
	long long start;
	int bytes = 0;
	int dir_count, size, res;
	struct dir_ent *ent, *cur_ent = NULL;
	struct dir *dir;

	TRACE("squashfs_opendir: inode start block %d, offset %d\n",
		block_start, offset);

	*i = read_inode(block_start, offset);

	dir = malloc(sizeof(struct dir));
	if(dir == NULL)
		MEM_ERROR();

	dir->dir_count = 0;
	dir->cur_entry = NULL;
	dir->mode = (*i)->mode;
	dir->uid = (*i)->uid;
	dir->guid = (*i)->gid;
	dir->mtime = (*i)->time;
	dir->xattr = (*i)->xattr;
	dir->dirs = NULL;

	if ((*i)->data == 0)
		/*
		 * if the directory is empty, skip the unnecessary
		 * lookup_entry, this fixes the corner case with
		 * completely empty filesystems where lookup_entry correctly
		 * returning -1 is incorrectly treated as an error
		 */
		return dir;

	start = sBlk.s.directory_table_start + (*i)->start;
	offset = (*i)->offset;
	size = (*i)->data + bytes;

	while(bytes < size) {
		if(swap) {
			squashfs_dir_header_2 sdirh;
			res = read_directory_data(&sdirh, &start, &offset, sizeof(sdirh));
			if(res)
				SQUASHFS_SWAP_DIR_HEADER_2(&dirh, &sdirh);
		} else
			res = read_directory_data(&dirh, &start, &offset, sizeof(dirh));

		if(res == FALSE)
			goto corrupted;

		dir_count = dirh.count + 1;
		TRACE("squashfs_opendir: Read directory header @ byte position "
			"%d, %d directory entries\n", bytes, dir_count);
		bytes += sizeof(dirh);

		/* dir_count should never be larger than SQUASHFS_DIR_COUNT */
		if(dir_count > SQUASHFS_DIR_COUNT) {
			ERROR("File system corrupted: too many entries in directory\n");
			goto corrupted;
		}

		while(dir_count--) {
			if(swap) {
				squashfs_dir_entry_2 sdire;
				res = read_directory_data(&sdire, &start,
					&offset, sizeof(sdire));
				if(res)
					SQUASHFS_SWAP_DIR_ENTRY_2(dire, &sdire);
			} else
				res = read_directory_data(dire, &start,
					&offset, sizeof(*dire));

			if(res == FALSE)
				goto corrupted;

			bytes += sizeof(*dire);

			/* size should never be SQUASHFS_NAME_LEN or larger */
			if(dire->size >= SQUASHFS_NAME_LEN) {
				ERROR("File system corrupted: filename too long\n");
				goto corrupted;
			}

			res = read_directory_data(dire->name, &start, &offset,
								dire->size + 1);

			if(res == FALSE)
				goto corrupted;

			dire->name[dire->size + 1] = '\0';

			/* check name for invalid characters (i.e /, ., ..) */
			if(check_name(dire->name, dire->size + 1) == FALSE) {
				ERROR("File system corrupted: invalid characters in name\n");
				goto corrupted;
			}

			TRACE("squashfs_opendir: directory entry %s, inode "
				"%d:%d, type %d\n", dire->name,
				dirh.start_block, dire->offset, dire->type);

			ent = malloc(sizeof(struct dir_ent));
			if(ent == NULL)
				MEM_ERROR();

			ent->name = strdup(dire->name);
			ent->start_block = dirh.start_block;
			ent->offset = dire->offset;
			ent->type = dire->type;
			ent->next = NULL;
			if(cur_ent == NULL)
				dir->dirs = ent;
			else
				cur_ent->next = ent;
			cur_ent = ent;
			dir->dir_count ++;
			bytes += dire->size + 1;
		}
	}

	return dir;

corrupted:
	squashfs_closedir(dir);
	return NULL;
}

Project: squashfs-tools

static struct dir *squashfs_opendir(unsigned int block_start, unsigned int offset,
	struct inode **i)
{
	squashfs_dir_header_3 dirh;
	char buffer[sizeof(squashfs_dir_entry_3) + SQUASHFS_NAME_LEN + 1]
		__attribute__((aligned));
	squashfs_dir_entry_3 *dire = (squashfs_dir_entry_3 *) buffer;
	long long start;
	int bytes = 0;
	int dir_count, size, res;
	struct dir_ent *ent, *cur_ent = NULL;
	struct dir *dir;

	TRACE("squashfs_opendir: inode start block %d, offset %d\n",
		block_start, offset);

	*i = read_inode(block_start, offset);

	dir = malloc(sizeof(struct dir));
	if(dir == NULL)
		MEM_ERROR();

	dir->dir_count = 0;
	dir->cur_entry = NULL;
	dir->mode = (*i)->mode;
	dir->uid = (*i)->uid;
	dir->guid = (*i)->gid;
	dir->mtime = (*i)->time;
	dir->xattr = (*i)->xattr;
	dir->dirs = NULL;

	if ((*i)->data == 3)
		/*
		 * if the directory is empty, skip the unnecessary
		 * lookup_entry, this fixes the corner case with
		 * completely empty filesystems where lookup_entry correctly
		 * returning -1 is incorrectly treated as an error
		 */
		return dir;

	start = sBlk.s.directory_table_start + (*i)->start;
	offset = (*i)->offset;
	size = (*i)->data + bytes - 3;

	while(bytes < size) {			
		if(swap) {
			squashfs_dir_header_3 sdirh;
			res = read_directory_data(&sdirh, &start, &offset, sizeof(sdirh));
			if(res)
				SQUASHFS_SWAP_DIR_HEADER_3(&dirh, &sdirh);
		} else
			res = read_directory_data(&dirh, &start, &offset, sizeof(dirh));
	
		if(res == FALSE)
			goto corrupted;

		dir_count = dirh.count + 1;
		TRACE("squashfs_opendir: Read directory header @ byte position "
			"%d, %d directory entries\n", bytes, dir_count);
		bytes += sizeof(dirh);

		/* dir_count should never be larger than SQUASHFS_DIR_COUNT */
		if(dir_count > SQUASHFS_DIR_COUNT) {
			ERROR("File system corrupted: too many entries in directory\n");
			goto corrupted;
		}

		while(dir_count--) {
			if(swap) {
				squashfs_dir_entry_3 sdire;
				res = read_directory_data(&sdire, &start,
					&offset, sizeof(sdire));
				if(res)
					SQUASHFS_SWAP_DIR_ENTRY_3(dire, &sdire);
			} else
				res = read_directory_data(dire, &start,
					&offset, sizeof(*dire));

			if(res == FALSE)
				goto corrupted;

			bytes += sizeof(*dire);

			/* size should never be SQUASHFS_NAME_LEN or larger */
			if(dire->size >= SQUASHFS_NAME_LEN) {
				ERROR("File system corrupted: filename too long\n");
				goto corrupted;
			}

			res = read_directory_data(dire->name, &start, &offset,
								dire->size + 1);

			if(res == FALSE)
				goto corrupted;

			dire->name[dire->size + 1] = '\0';

			/* check name for invalid characters (i.e /, ., ..) */
			if(check_name(dire->name, dire->size + 1) == FALSE) {
				ERROR("File system corrupted: invalid characters in name\n");
				goto corrupted;
			}

			TRACE("squashfs_opendir: directory entry %s, inode "
				"%d:%d, type %d\n", dire->name,
				dirh.start_block, dire->offset, dire->type);

			ent = malloc(sizeof(struct dir_ent));
			if(ent == NULL)
				MEM_ERROR();

			ent->name = strdup(dire->name);
			ent->start_block = dirh.start_block;
			ent->offset = dire->offset;
			ent->type = dire->type;
			ent->next = NULL;
			if(cur_ent == NULL)
				dir->dirs = ent;
			else
				cur_ent->next = ent;
			cur_ent = ent;
			dir->dir_count ++;
			bytes += dire->size + 1;
		}
	}

	return dir;

corrupted:
	squashfs_closedir(dir);
	return NULL;
}

Project: squashfs-tools

static struct dir *squashfs_opendir(unsigned int block_start, unsigned int offset,
	struct inode **i)
{
	struct squashfs_dir_header dirh;
	char buffer[sizeof(struct squashfs_dir_entry) + SQUASHFS_NAME_LEN + 1]
		__attribute__((aligned));
	struct squashfs_dir_entry *dire = (struct squashfs_dir_entry *) buffer;
	long long start;
	int bytes = 0, dir_count, size, res;
	struct dir_ent *ent, *cur_ent = NULL;
	struct dir *dir;

	TRACE("squashfs_opendir: inode start block %d, offset %d\n",
		block_start, offset);

	*i = read_inode(block_start, offset);

	dir = malloc(sizeof(struct dir));
	if(dir == NULL)
		MEM_ERROR();

	dir->dir_count = 0;
	dir->cur_entry = NULL;
	dir->mode = (*i)->mode;
	dir->uid = (*i)->uid;
	dir->guid = (*i)->gid;
	dir->mtime = (*i)->time;
	dir->xattr = (*i)->xattr;
	dir->dirs = NULL;

	if ((*i)->data == 3)
		/*
		 * if the directory is empty, skip the unnecessary
		 * lookup_entry, this fixes the corner case with
		 * completely empty filesystems where lookup_entry correctly
		 * returning -1 is incorrectly treated as an error
		 */
		return dir;

	start = sBlk.s.directory_table_start + (*i)->start;
	offset = (*i)->offset;
	size = (*i)->data + bytes - 3;

	while(bytes < size) {			
		res = read_directory_data(&dirh, &start, &offset, sizeof(dirh));
		if(res == FALSE)
			goto corrupted;

		SQUASHFS_INSWAP_DIR_HEADER(&dirh);
	
		dir_count = dirh.count + 1;
		TRACE("squashfs_opendir: Read directory header @ byte position "
			"%d, %d directory entries\n", bytes, dir_count);
		bytes += sizeof(dirh);

		/* dir_count should never be larger than SQUASHFS_DIR_COUNT */
		if(dir_count > SQUASHFS_DIR_COUNT) {
			ERROR("File system corrupted: too many entries in directory\n");
			goto corrupted;
		}

		while(dir_count--) {
			res = read_directory_data(dire, &start, &offset, sizeof(*dire));
			if(res == FALSE)
				goto corrupted;

			SQUASHFS_INSWAP_DIR_ENTRY(dire);

			bytes += sizeof(*dire);

			/* size should never be SQUASHFS_NAME_LEN or larger */
			if(dire->size >= SQUASHFS_NAME_LEN) {
				ERROR("File system corrupted: filename too long\n");
				goto corrupted;
			}

			res = read_directory_data(dire->name, &start, &offset,
								dire->size + 1);
			if(res == FALSE)
				goto corrupted;

			dire->name[dire->size + 1] = '\0';

			/* check name for invalid characters (i.e /, ., ..) */
			if(check_name(dire->name, dire->size + 1) == FALSE) {
				ERROR("File system corrupted: invalid characters in name\n");
				goto corrupted;
			}

			TRACE("squashfs_opendir: directory entry %s, inode "
				"%d:%d, type %d\n", dire->name,
				dirh.start_block, dire->offset, dire->type);

			ent = malloc(sizeof(struct dir_ent));
			if(ent == NULL)
				MEM_ERROR();

			ent->name = strdup(dire->name);
			ent->start_block = dirh.start_block;
			ent->offset = dire->offset;
			ent->type = dire->type;
			ent->next = NULL;
			if(cur_ent == NULL)
				dir->dirs = ent;
			else
				cur_ent->next = ent;
			cur_ent = ent;
			dir->dir_count ++;
			bytes += dire->size + 1;
		}
	}

	return dir;

corrupted:
	squashfs_closedir(dir);
	return NULL;
}